Trump Could Be A Real Drag On GOP: Here Are The Top 10 Senate Races To Watch

Aside from the White House race, there's another important battle this November that shouldn't be overlooked — the fight for control of the U.S. Senate.

Republicans won back the majority just two years ago after eight years in the political wilderness. But they could just as easily lose that newfound power, especially if a controversial GOP nominee like Donald Trump is at the top of the ticket. Republicans believe that likely Democratic nominee Hillary Clinton could also damage some Democrats, though, with low approval ratings herself and the shadow of her email scandal still lingering. But they acknowledge that the math isn't in their favor and that they will lose ground.

First, here's the starting line: Republicans have a 54-to-46 seat advantage (two independents caucus with the Democrats). That means Democrats need to flip four seats if they win the presidency. (The vice president is president of the Senate and casts the tiebreaking vote.) If they lose, they need to pick up five for control. That's a very doable task given the map. It's also a presidential year, when key Democratic demographic groups, like young voters and single women, turn out in higher numbers than in midterm years.

Because of that, the math and the map in 2014 heavily favored Republicans. Democrats were defending 21 seats, while Republicans had just 15 up. The opposite is true in 2016. The GOP is defending 24 seats compared with just 10 for Democrats. Republicans are defending seats in seven states President Obama carried in 2012, and most of them will be White House battlegrounds again — Florida, New Hampshire, Ohio, Pennsylvania and Wisconsin.

Six months out from Election Day, NPR is premiering its Top 10 Senate seats most likely to flip control. Notably, because of the map and the number of GOP seats in play, nine on this list are Republican-held seats. These lists will be based on our reporting with the campaigns and campaign committees on both sides, as well as public and private polling — and reporting from the field. We'll be updating it at the first of each month. Here are our inaugural rankings:

1. Illinois (R-Kirk): Incumbent Mark Kirk has the unlucky distinction of being the Republican senator representing the bluest state in his caucus. The former representative notched a bipartisan record in the House but only narrowly won this Senate seat in 2010. That was a GOP wave year, and he faced a scandal-plagued Democratic nominee. It's a different story in this presidential year. He's facing Democrat Tammy Duckworth, a two-term representative and Iraq veteran who lost both her legs in a helicopter crash. Kirk had a major health setback in 2011 when he suffered a stroke. It has left him with some limited mobility, but he has recovered well.

2. Wisconsin (R-Johnson): Unlike Kirk or some of his other vulnerable colleagues, freshman Sen. Ron Johnson hasn't built a moderate profile and really hasn't tried to move to the center at all. That won't help him in a presidential year, when Wisconsin leans Democratic. Wisconsin hasn't gone Republican for president in 32 years. That's very different than the 2010 environment that helped Johnson, a wealthy plastics manufacturer, unseat Democratic Sen. Russ Feingold. And guess who's seeking a rematch? The progressive favorite is polling ahead of Johnson in early surveys, though the race has tightened. As with Kirk, with a GOP led by Trump at the top of the ticket, the odds move more in Feingold's favor.

3. New Hampshire (R-Ayotte): The next four contests are just narrowly separated. But with the Granite State being a presidential tossup state, this race between incumbent GOP Sen. Kelly Ayotte and Democratic Gov. Maggie Hassan will be one of the marquee races this cycle. A WMUR poll last month showed the race was a virtual dead heat, and the Republican was leading handily with independents. But Ayotte's decision to join Senate Republicans in a refusal to consider President Obama's Supreme Court nominee, Merrick Garland, has hurt her approval ratings, according to the survey.

4. Pennsylvania (R-Toomey): National Democrats got a boost last week when their favored candidate, former state environmental chief Katie McGinty, won a competitive primary over 2010 Democratic nominee Joe Sestak. Incumbent Pat Toomey, a former president of the conservative Club for Growth, narrowly defeated Sestak in the open race that year. The bitter Democratic primary this year was a costly endeavor. The Democratic Senatorial Campaign Committee spent more than $1 million to boost McGinty over Sestak, and her own campaign coffers were significantly depleted. Toomey, meanwhile, has $9.1 million in the bank, and he has looked to boost his moderate credentials for his work on gun control legislation and support for universal background checks. Pennsylvania has never elected a woman as governor or to the Senate, but Democrats think that will change with a woman as their nominee and especially if Trump is at the top of the ticket for the GOP.

5. Ohio (R-Portman): This race is another matchup of two titans, with GOP Sen. Rob Portman defending his seat from former Gov. Ted Strickland. John Kasich narrowly defeated Strickland for governor in the GOP wave year of 2010. Portman has a mammoth $13.4 million war chest for what's sure to be a close, expensive and nasty contest. Democrats want to redefine Portman as a GOP stalwart instead of allowing him to portray himself as bipartisan. They are also banking on Portman being dragged down by Trump at the top of the ticket. Portman, on the other hand, is already hitting Strickland for his jobs record as governor. Republicans also want to want to chip away at the crossover credentials Strickland was able to hone especially in rural parts of the state.

6. Florida (R-open, Rubio not seeking re-election): There's an argument to put this race higher up on the list, but until both parties settle their primaries in August it's harder to handicap the outcome. Democrats are praying Rep. Patrick Murphy beats controversial fellow Rep. Alan Grayson, who is under an ethics investigation for allegedly improperly using his office and influence with a hedge fund he managed. Even with that significant baggage, Grayson remains popular with progressives and, by all accounts, the primary is tight.

Republicans don't have a clear nominee either, though, with four main candidates emerging. Rep. Ron DeSantis has conservative support, while Rep. David Jolly, a former state lobbyist, is on the outs with the party after he participated in a controversial "60 Minutes" story to tout his bill that would ban lawmakers from raising campaign cash. He attended a fundraiser for his campaign just days later. Lt. Gov. Carlos Lopez-Cantera had initially seemed like a strong candidate but has had trouble raising funds. Republicans now say to keep an eye on wealthy homebuilder Carlos Beruff, who has said he intends to largely self-fund his campaign and is already up on TV in the state. Ultimately, until either party settles on a nominee, it's hard to predict where this one rightfully sits on the list.

7. Nevada (D-open, Reid retiring): This is Republicans' best (and some might say only) pickup opportunity this cycle. They were already targeting this seat, but their chances got a lot better when Senate Minority Leader Harry Reid announced his retirement. Former Attorney General Catherine Cortez Masto should easily win her primary next month on the Democratic side. If she wins in November, she would be the first Latina in the Senate. Republicans' favored candidate, Rep. Joe Heck, should easily beat back a challenge from controversial 2010 nominee Sharron Angle. The Cortez Masto-Heck race will be a close one, but if Hispanic voters are very motivated to go to the polls to vote against Trump, this pickup becomes much harder for Republicans. (Hispanics were almost 1 in 5 voters in the 2012 Senate election.)

8. Missouri (R-Blunt): This contest in the Show Me State might be the dark-horse contest to watch. Democrats got one of their best recruits this cycle when Secretary of State Jason Kander jumped in the race. Even Republicans privately admit that the 34-year-old Afghanistan veteran worries them running against Sen. Roy Blunt, whom Democrats are eager to paint as too much of a Washington insider. If Missouri comes in play in the presidential race, this one could quickly give Republicans a huge headache.

9. North Carolina (R-Burr): The Tar Heel State is moving up on both parties' lists amid the flurry of controversy over the state's anti-discrimination law, commonly referred to as the "bathroom bill." That law blocks transgender persons from using the bathroom that corresponds with the gender with which they identify. Former state Rep. Deborah Ross certainly wasn't Democrats' top choice to challenge Sen. Richard Burr, but she did outraise him in the first fundraising quarter. The incumbent, however, still has a cash advantage with $5.8 million in the bank. If this one emerges as a presidential battleground (remember, Obama won it in 2008), it could certainly have down-ballot effects.

10. (tie) Arizona (R-McCain)/Colorado (D-Bennet): Arizona is another contest that's been under the national political radar but might not stay there for long. Early on, it seemed like 2008 presidential nominee John McCain's biggest threat against winning a sixth term would be a GOP primary challenger. That shouldn't be a problem after several congressmen passed, but Democratic Rep. Ann Kirkpatrick could be a tougher-than-expected rival. She has managed to win two tough congressional races in red districts (after losing in 2010), and even Republicans admit she shouldn't be underestimated any longer. Polls show this one is close, but Democrats have tried to make Senate races competitive in the state with good recruits before and failed. Arizona still leans Republican in a presidential year, but if there are new Hispanic voters energized against Trump's candidacy, that could certainly hurt McCain.

In Colorado, just a few days ago, this contest to unseat Democratic Sen. Michael Bennet may have been higher on the list. But then several top GOP recruits failed to make the ballot last week. Former state Rep. Jon Keyser did successfully get reinstated after he initially fell 86 signatures short on his petitions. Both wealthy businessman Robert Blaha and former Aurora city councilman Ryan Frazier are also suing to get back on the ballot after some of their signatures were deemed invalid. The bottom line is that Republicans needed another strong recruit like now-Sen. Cory Gardner, who knocked off a Democratic incumbent last cycle. Even before the ballot snafus of the trio of Republicans, they didn't get a clear top candidate. Bennet has proved to be a good fundraiser and candidate in the past, winning a tough race for a full term in an uphill battle in 2010.

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